Defmt Logging

[bjackson312006]

This PR adds support for this library, which replicates the functionality of the defmt Rust crate, but for C projects.

Aside from just including the library as a submodule, this PR adds a new ner cdefmt command to run the decoder for you. The first time you run ner cdefmt, it will have to actually build the decoder for you, so you'll need to have cargo installed. Also, make sure to turn off any existing printf()->UART before trying to use cdefmt, since the decoder has no idea how to interpret normal printf()s and you'll get an error when you run ner cdefmt.

Here's a copy of the README I made to explain how to actually start using cdefmt logging in NER projects:

Setting Up cdefmt

To set up CDEFMT logging in an existing project, there are a few steps you need to follow.

First, make sure the project has Embedded-Base as a submodule, on a commit that has cdefmt_port included. You'll need to run git submodule update --init --recursive to make sure the cdefmt library is pulled.

Then, add this to the parent project's top-level CMakeLists.txt:

add_subdirectory(Drivers/Embedded-Base/cdefmt_port)

target_link_libraries(${CMAKE_PROJECT_NAME}
    embedded_base_cdefmt
    # ... other libs ...
)

After that, add the cdefmt routing code to your project's main.c:

#include <cdefmt/include/cdefmt.h>

/* Emits the static-inline `cdefmt_init()` function used during start-up to
 * send the build-id init log. Must appear at file scope exactly once in the
 * whole program. */
CDEFMT_GENERATE_INIT();

/**
 * @brief Transport sink invoked by every CDEFMT_* macro.
 */
void cdefmt_log(const void *log, size_t size, enum cdefmt_level level)
{
    (void)level; /* Runtime level filtering can be added here if desired. */

    const uint64_t hdr = (uint64_t)size;

    HAL_UART_Transmit(&huart2, (uint8_t *)&hdr, sizeof hdr, HAL_MAX_DELAY);
    HAL_UART_Transmit(&huart2, (uint8_t *)log, (uint16_t)size, HAL_MAX_DELAY);
}

(Obviously, you should use whatever UART your project has available, rather than specifically huart2. Also, make sure nothing else is using this UART aside from cdefmt; if you also have printf() routed to this same UART or something, you'll get errors when trying to run ner cdefmt.)

Also, add cdefmt_init() to the main() function in your main.c, after your UART initialization code has ran.

Usage

Now, you should be ready to use cdefmt. In any file where you want to log stuff, add #include <cdefmt/include/cdefmt.h> to the top. Then, you can use the following cdefmt macros:

CDEFMT_ERROR("This is an error log.");
CDEFMT_WARNING("This is a warning log.");
CDEFMT_INFO("This is an info log.");
CDEFMT_DEBUG("This is a debug log.");
CDEFMT_VERBOSE("This is a verbose log.");

Here's an example of how formatting data works in these macros:

CDEFMT_DEBUG("loop state: tick={} led_pin={:#x}, cool_float={}", tick, led_pin, cool_float);
// `tick` is a uint32_t, `led_pin` is a uint16_t that we want to display in hex, and `cool_float` is a float

That macro call produced this log when I ran the code and viewed logging output (via ner cdefmt):

[u_threads.c/vDefault():78] Debug   > loop state: tick=17 led_pin=0x20, cool_float=64.08844

As shown above, the logs are automatically prepended with the filename, function name, line number, and logging level (e.g., Debug, Warning, Error, etc) corresponding to the macro call.

Other Important Stuff

• Using cdefmt requires cargo, since the decoder will need to get built on your device.
• It may be helpful to run ner cdefmt --rebuild if you run into issues, since this will rebuild the decoder on your device.
• Again, you NEED to give cdefmt its own dedicated UART (or just disable printf()-to-UART routing) for ner cdefmt to work. If ner cdefmt encounters non-defmt prints when trying to decode, it will fail.